Thank you for posting here in the Community, @Simon_thehub.
In QuickBooks Online, the Employer Settings option is visible when you click the Cogwheel ⚙️ icon found in the upper-right corner. As long as you have the right region, you'll be able to turn on the option from your account.
For additional information, I've attached an article about turning on employment allowance and how to submit an EPS to HMRC: Employment Allowance.
I'm only a few clicks away if you have any other questions. Wishing you and your business continued success.